Positive Halogens from Halides and Hydrogen Peroxide with Organotellurium Catalysts

Abstract

The oxidations of sodium bromide, sodium chloride, and sodium iodide to positive halogen with hydrogen peroxide in two-phase systems of dichloromethane and pH 6 phosphate buffer were catalyzed by organotellurium catalysts 1−3. The positive halogens were trapped by cyclohexene for bromine and chlorine to give mixtures of the 1,2-dihalocyclohexane (4) and 2-halocyclohexanol (5). For the bromination (4a)/hydrobromination (5a) of cyclohexene, unoptimized turnover numbers of 1010 mol of product per mole of catalyst for 1, 960 for 2, and 820 for 3 were measured with 4a/5a ratios of 55:45, 53:47, and 52:48, respectively. In cyclohexane, the turnover number for 1 was 150 and the 4a/5a ratio was 68:32. In the uncatalyzed process and in the reaction of aqueous bromine with cyclohexene, the 4a/5a ratio is 55:45 in dichloromethane and 67:33 in cyclohexane. The relative rates of catalysis for equimolar amounts of 1−3 were nearly identical to the relative second-order rate constants for oxidation of the organotellurium...